Abstract
One-dimensional ZnO nanowires (NWs) are a promising materials system for a variety of applications. Utilization of ZnO, however, requires a good understanding and control of material properties that are largely affected by intrinsic defects and contaminants. In this work we provide experimental evidence for unintentional incorporation of nitrogen in ZnO NWs grown by rapid thermal chemical vapor deposition, from electron paramagnetic resonance spectroscopy. The incorporated nitrogen atoms are concluded to mainly reside at oxygen sites (NO). The NO centers are suggested to be located in proximity to the NW surface, based on their reduced optical ionization energy as compared with that in bulk. This implies a lower defect formation energy at the NW surface as compared with its bulk value, consistent with theoretical predictions. The revealed facilitated incorporation of nitrogen in ZnO nanostructures may be advantageous for realizing p-type conducting ZnO via N doping. The awareness of this process can also help to prevent such unintentional doping in structures with desired n-type conductivity.
Highlights
Unknown, it could be caused by formation of complexes with residual defect/impurities
Two single-line EPR signals labeled as A and B in Fig. 2 can be observed
White light illumination leads to appearance of another EPR signal that consists of three spaced lines, which is characteristic for a resolved hyperfine interaction involving a nucleus spin I = 1 with natural abundance of 100%
Summary
Unknown, it could be caused by formation of complexes with residual defect/impurities. The energy level of the N acceptor can be affected by its local surrounding[30], complexing with residual group III impurities[31] and defects[32,33], as well as formation of N-N molecules[34]. Growth conditions utilized during the NW growth may facilitate dopant incorporation leading to higher dopability of these materials. In this letter we employ magnetic resonance spectroscopy[35] to investigate defect formation processes in nominally undoped ZnO NWs grown by chemical vapor deposition, aiming to single out chemical origin of incorporated contaminants
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